S. National Institutes of Health (grant number Indian Health Service NARCH III U26IHS300012,); and the National Cancer Institute at the National Institutes of Health (contract number HHSN261200700462P) and grant number CA114609. Declaration of Interests Dorothy K. Hatsukami, inhibitor Ganetespib Ph.D., of the University of Minnesota, was funded for by Nabi Biopharmaceuticals and NIDA to be a site for a multi-site clinical trial for a nicotine vaccine. Dr. Rachel F. Tyndale owns shares and participates in Nicogen Research Inc., a company focused on novel smoking cessation treatment approaches. No Nicogen funds were used in this work and no other Nicogen participants reviewed the data. Dr. Tyndale has also consulted for one day for Novartis and McNeil. Dr. Neal L. Benowitz serves as a consultant to Pfizer Pharmaceuticals, Inc.

and has been a paid expert witness in litigation against tobacco companies. This research was not supported by industry funds. Acknowledgments The scientific team would like to express their gratitude for the leadership and direction from the members of the Board of Directors of the Bristol Bay Area Health Corporation, the members of the Ethics Committee of that organization and the Community Advisory Board for this study, and the BBAHC Director of Community Health Services, Ms. Rose Loera, Ms. Shelly Wallace, all who contributed their time and expertise to making this study possible. We would also like to acknowledge contributions of Ms. Kim Hatt, Ms. Ana Chartier and Ms. Helen Peters who were study assistants to the project. In addition, we would like to acknowledge Drs.

David Ashley and Tom Bernert for advice on study design and Ms. Christie Flanagan for her assistance in manuscript preparation.
Introduction: Studies suggest that initial smoking pleasure influences future smoking behavior. We investigated how initial reactions to cigarettes or Swedish smokeless tobacco (snus) were associated with future use among 10,708 adults from the Swedish Twin Registry. Methods: The Early Smoking Experience questionnaire captured physiologic reactions to initial tobacco use. Binary recursive partitioning (BRP) identified combinations of initial reactions predictive of regular tobacco use. Analyses, stratified by sex, were conducted separately among those who experimented with only cigarettes (EC), only snus (ES), and both products (EC+S). Results: Among EC, 39.

8% of men and 43.7% of women became smokers, while among ES, 78.6% of men and 53.7% of women became snus users. Among EC+S, 31.3% of men and 20.0% of women became dual users. BRP identified different reactions as predictive of future smoking Dacomitinib for men (buzz) and women (dizziness, difficulty inhaling). No initial reaction predicted future snus use among men, but pleasant sensations, later age at first use, and relaxation predicted future snus use for women.